Reexamining Rates of Decline in Lung Cancer Risk after Smoking Cessation: A meta-analysis.

RATIONALE Prior studies have questioned whether prevailing eligibility criteria for lung cancer screening are sufficiently inclusive of former smokers who remain at elevated risk of disease outside current screening windows. OBJECTIVE Characterize the percent of the reducible relative risk remaining (RRR) for lung cancer as a function of years since quitting. METHODS MEDLINE and PubMed were searched from January 2011 to May 2018; key search terms included smoking and cancer. Current smoker relative risks were extracted to represent former smokers at zero years since quitting; data were transformed assuming a lognormal distribution. RESULTS The main review included 49 prospective cohorts across 18 studies comprising a total of 139 RRs from 20 countries and territories. At one year since quitting, the percentage of RRR for lung cancer was 81.4% [64.1-98.2]. At five years since quitting, RRR was 57.2% [45.7-67.3]; at 10 years: 36.9% [28.3-47.9]; at 15 years, 26.7% [20.2-34.3]; at 20 years, 19.7% [13.3-26.4]. If eligibility criteria in the US were broadened to screen former smokers up to 20 years since quitting, we estimate an additional 4.2 [3.9-4.5] million former smokers between 55-80 years of age would be eligible for lung cancer screening. CONCLUSION At the critical screening threshold of 15 years since quitting, the percentage of excess risk for lung cancer remains high and only marginally declines at time points afterward, excluding millions of former smokers who remain at elevated risk of malignancy. A risk-based screening algorithm for lung cancer screening that de-emphasizes time post-cessation as a key screening determinant would more likely capture these former smokers who remain at elevated risk of malignancy.